Image compressing method, image reconstructing method, image compressing device, image reconstructing device, image compressing program product, and image reconstructing program product

ABSTRACT

A method includes: a splitting step in which a full-screen image data acquired in a full-screen image acquiring step is split into block images in a predetermined size from one end of a screen area; a positional information creating step in which block images at two sequential time instants are compared in every block image split in the splitting step to create positional information data expressing presence or absence of a difference and positional information about a block considered to have a difference; and a compressed difference image creating step in which a block determined as a block considered to have a difference in the positional information creating step is a difference block, and an image collection created by arranging block images of difference blocks at the identical time instant is compressed as one image to create a compressed difference image.

TECHNICAL FIELD

The present disclosure relates to a screen image transfer method thattransfers an image displayed on a computer screen and a screen imagereconstructing method that reconstructs a transferred screen image intoan original image.

BACKGROUND ART

Conventionally, image processing is known as screen image transfermethods of transferring, to another device (e.g. a recording server),the content on the screen of the display of the personal computer (PC)that is changed over time due to use, for example, in real time. Inorder to avoid an increase in data volumes due to transfer of image datain the bitmap format, the image processing includes reducing resolution,reducing gray scale level of colors, and roughening pictures bytransferring image data that is converted into JPEG format, bytransferring only differences, or by transferring differences that areconverted into JPEG format (e.g. see JP 2009-10871 A).

SUMMARY OF INVENTION

An image compressing method according to an aspect of the presentdisclosure includes: a full-screen image acquiring step in whichfull-screen image data displayed on a screen of a display issequentially acquired; a compressed full-screen image creating step inwhich a full-screen image acquired every predetermined recording timeperiod in the full-screen image acquiring step is compressed to create acompressed full-screen image; a splitting step in which the full-screenimage data acquired in the full-screen image acquiring step is splitinto block images from one end of a screen area; a positionalinformation creating step in which block images at two sequential timeinstants are compared in every block images split in the splitting stepto create positional information data expressing presence or absence ofa difference and positional information about a block considered to havea difference; and a compressed difference image creating step in which ablock determined as a block considered to have a difference in thepositional information creating step is a difference block, and an imagecollection created by arranging block images of difference blocks at anidentical time instant is compressed as one image to create a compresseddifference image.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing an exemplary system configuration of apersonal computer (PC) screen monitoring system using a first embodimentof a screen image transfer method according to an exemplary embodiment.

FIG. 2 is a block diagram of a recording PC of the first embodiment ofthe screen image transfer method according to the exemplary embodiment.

FIG. 3 is a conceptual diagram when a difference image on the recordingPC is created in the first embodiment of the screen image transfermethod according to the exemplary embodiment.

FIG. 4 is a block diagram of a recording server of the first embodimentof the screen image transfer method according to the exemplaryembodiment.

FIG. 5 is an illustration of a transfer method from the recording PC tothe recording server and a saving method on the recording server in aflow of the first embodiment of the screen image transfer methodaccording to the exemplary embodiment.

FIG. 6 is a block diagram of a terminal (mobile terminal) of the firstembodiment of the screen image transfer method according to theexemplary embodiment.

FIG. 7 is a block diagram of a terminal (PC) of the first embodiment ofthe screen image transfer method according to the exemplary embodiment.

FIG. 8 is a flowchart showing the outline of procedures from capturingthe screen of the recording PC to accumulation on the recording serverin the first embodiment of the screen image transfer method according tothe exemplary embodiment.

FIG. 9 is a flowchart showing the outline of procedures from capturingthe screen of a recording PC to accumulation on a recording server of asecond embodiment of the screen image transfer method according to theexemplary embodiment.

DESCRIPTION OF EMBODIMENTS

However, the conventional screen image transfer method has a problemthat volumes are immeasurably increased in data transfer in the bitmapformat. In order to avoid this problem, in transfer in which the formatis converted into the JPEG format, there is a problem that volumes aremade small by increasing JPEG compression ratios or by reducingresolution, resulting in a decrease in resolution, for example.

In a method that detects only areas where changes are observed(differences) with no change in resolution for data transfer in order toavoid the problem of resolution decrease, volumes are decreased or bydecreasing the number of colors or by devising data formats, forexample. However, this method has problems that the load of a PCprocessing data is prone to increase and volumes are not decreasedsufficiently.

That is, the conventional screen image transfer methods have problemsthat compression or decompression causes a reduction in resolution todegrade images, that data volumes to be transferred are large, or thatthe load of the PC processing data is increased.

Therefore, an object of the exemplary embodiment is to solve theproblems above and to provide a screen image transfer method that canprevent the image quality of a screen image on the display of a personalcomputer from being degraded and can efficiently transfer the screenimage, and enables a decrease in the load of the PC processing data.

In order to achieve the object, a first aspect of the exemplaryembodiment is to provide a screen image transfer method that causes apersonal computer connected to the server via the network to execute: afull-screen image acquiring step in which full-screen image datadisplayed on a screen of a display is acquired every certain timeinterval; a compressed full-screen image creating step in which afull-screen image acquired every predetermined recording time period inthe full-screen image acquiring step is JPEG-compressed to create andaccumulate a compressed full-screen image, a compressed full-screenimage is not created until a lapse of a predetermined recording timeperiod every time when a compressed full-screen image is created, andthe step goes to a subsequent step; a full-screen image transferringstep in which a full screen data file including the compressedfull-screen image created in the full-screen image creating step iscreated and the full screen data file is transferred to the server; asplitting step in which the full-screen image data acquired in thefull-screen image acquiring step is split into block images of a matrixof eight by eight picture elements from one end of a screen area; apositional information creating step in which block images at twosequential time instants are compared in every block image split in thesplitting step to create positional information data expressing presenceor absence of a difference and positional information about a blockconsidered to have a difference based on a block sequential number; aparallel number calculating step in which a block determined as a blockconsidered to have a difference in the positional information creatingstep is categorized into a difference block to calculate, from thenumber of difference blocks at an identical time instant, the number ofparallel blocks to be horizontally arranged in order to form a rectanglewith the smallest margin by arranging all block images of the differenceblocks at the identical time instant; a compressed difference imagecreating step in which a step is repeated in which the block images ofthe difference blocks in the number of the parallel blocks calculated inthe parallel number calculating step are horizontally arranged and thenarranged on the under side, an image collection in a rectangle with themargin blanked is created, the collection is JPEG-compressed as oneimage, and the compressed difference image is created and accumulated;and a difference image transferring step in which a difference data fileincluding the compressed difference image and pieces of positionalinformation data is created and the file is transferred to the server.

According to the first aspect of the exemplary embodiment, one imagecomposed only of difference images is JPEG-compressed and transferred.Thus, the image quality of the screen image on the display of thepersonal computer can be prevented from being degraded, the screen imagecan be efficiently transferred, and a decrease in the load of the PCprocessing data is enabled.

Note that the term “image” includes meanings of both of a still imageand a moving image. In the present application, the still image isexpressed as “image”, and the moving image is expressed as “picture” fordistinguishing between the images.

The block image of a matrix of eight by eight picture elements is animage in the minimum unit of the JPEG component, and the image is in themost efficient size in the steps of compression, transfer, anddecompression.

In the positional information creating step, in the comparison, a hashvalue is generated for each block image and compared, a block with anunequal calculated value is categorized into a block with a difference,and a block with an equal calculated value is categorized into a blockwith no difference. The positional information data is preferably onebyte data or two byte data in which a first one bit expresses presenceor absence of a difference and seven bits or 15 bits express a number ofcontinuous blocks in which the presence or absence of difference is thesame.

The data volumes of positional information to be transferred can beconsiderably made small. Note that the positional information data maybe coordinates data on the display. There is a merit that although datavolumes are large, positions are grasped by only seeing data.

Until a lapse of the predetermined recording time period, the steps fromthe full-screen image acquiring step to the compressed difference imagecreating step are repeated except the full-screen image transferringstep. After that, instead of the compressed difference imagetransferring step, an accumulated image transferring step is preferablyincluded in which an accumulation data file including the compressedfull-screen image, the compressed difference images accumulated until alapse of a predetermined recording time period, and pieces of positionalinformation data is created and the file is transferred to the server.

Unnecessary header information can be decreased, and the minimuminformation volume is used.

Alternatively, the steps from the screen image acquiring step to thedifference image transferring step may be repeated every certain timeinterval.

The difference data file is transferred every time, and hence browse inreal time is enabled, although the information volume of headerinformation is increased.

A second aspect of the exemplary embodiment is to provide areconstructing method for an image transferred to a server by the screenimage transfer method of the first aspect of the exemplary embodimentdescribed above, the reconstructing method including:

a difference block reconstructing step in which the image collection isreconstructed from the compressed difference image to reconstruct blockimages of difference blocks; and

a full-screen image reconstructing step of repeating a step for thepredetermined recording time period in which the block image of thedifference block is placed on a full-screen image at a previous timeinstant based on the positional information data to create a full-screenimage at subsequent time instant.

According to the second aspect of the exemplary embodiment, an image ofhigh resolution can be reconstructed, and hence a moving image of highresolution can be replayed.

In the present disclosure, the term “network” includes networksconfigured of communication networks, such as local area networks(LANs), the Internet, Wireless-Fidelity (Wi-Fi) circuits, thirdgeneration (3G) long-term evolution (LTE) circuits, and leased circuits,and combinations of these circuits. A group of the displays (recordingPCs) of personal computers on the recorded side does not have to beconnected to the recording server via LAN networks, even a recording PCconnected to the Internet thought 3G/LTE circuits can considerablyreduce the information volume of data that can replay moving images ofhigh resolution after reconstruction and can transfer the data to therecording server, increasing the range of monitorable PCs. Note that therecording server may be a cloud server. More preferably, the movingimage compression format of images acquired from the recording PC groupis the H.264 format that provides high compression at the present pointin time. The device is light-weight, and easily mounted on any ofhardware and software.

According to the exemplary embodiment, the image quality of the screenimage on the display of the personal computer can be prevented frombeing degraded, the screen image can be efficiently transferred, and adecrease in the load of the PC processing data is enabled.

In the following, the exemplary embodiment will be described more indetail using embodiments. However, these embodiments do not limit theexemplary embodiment.

First Embodiment

Configuration

The screen of the display of a personal computer (PC) that is an exampleof image compressing devices changes every moment due to the use of thePC or execution of programs by a user, for example. A screen imagetransfer method according to a first embodiment of the exemplaryembodiment and an image reconstructing method according to the firstembodiment are methods usable for a PC screen monitoring system thatmonitors one or a plurality of such PC screens for monitoring.

In the embodiment, the term “recording PC” is a personal computer thattransfers screen images to a recording server that is an example of animage reconstructing device connected via a network and is a target tobe monitored.

The screen image transfer method according to the first embodiment ofthe exemplary embodiment is a screen image transfer method with whichthe recording PC connected to the recording server via the networktransfers screen images combined in a predetermined recording timeperiod to the recording server. The image reconstructing methodaccording to the first embodiment of the exemplary embodiment is amethod with which the recording server edits images gathered on therecording server in accordance with the screen image transfer methodaccording to the first embodiment of the exemplary embodiment andreconstructs the images. These methods enable saving, on the recordingserver, the images reconstructed by the image reconstructing methodaccording to the first embodiment of the exemplary embodiment, andenable transmission of images on the recording PC monitored via thenetwork from the recording server to a monitoring user terminal.

The PC screen monitoring system transmits images reconstructed by theimage reconstructing method according to the first embodiment, and thesystem replays, rewinds, and fast-forwards live images, and replayslibraries as well. In the embodiment, images on the screen of therecording PC can be made in a considerably small size for a certain timeperiod as well as difference images. Thus, information volumes to betransferred can be decreased at the minimum, volumes transferred fromthe recording PC to the recording server can be made small, andgathering of the screen images of the recording PC is enabled with norecording server installed at a local site. Data volumes oncommunications can be decreased, compared with simple gathering ofscreen images of the recording PC, a load on the network is small, aswell as monitoring with images of high resolution is enabled when imagesare reconstructed.

In the screen image transfer method according to the first embodiment ofthe exemplary embodiment, the JPEG properties are exploited in whichimage are not affected by images in the adjacent blocks in compressionand decompression of images in a block unit. Thus, the minimum imagedegradation is achieved, JPEG is adopted, images are compressed, andhence another compression process is eliminated. That is, from thefindings, the processes conventionally performed can be eliminated bysolving problems how to reduce data volumes and how to compress reduceddata based on the JPEG format. The states are achieved in which blockswith differences are converted into JPEG images as they are with nochange in the number of colors or data formats, and hence differencedata can be automatically created in the minimum time as well as ahighly compressed state is achieved.

FIG. 1 is a diagram showing an exemplary system configuration of a PCscreen monitoring system using the first embodiment of the screen imagetransfer method according to the exemplary embodiment. On a network 500composed of a combination of communication networks, such as LANs, theInternet, Wi-Fi circuits, 3G/LTE circuits, and leased circuits, thefollowing is connected: (1) a plurality of recording PCs 400A to 400Fthat are monitor targets;

-   (2) a recording server 100 that is connected to the recording PCs    400A to 400F through the network 500, acquires and accumulates image    data from the recording PC 400, and transmits the data to a    terminal; and-   (3) mobile terminals 200A and 200B, such as smartphones, and    browsing PCs 300A to 300C, such as desktop personal computers (PCs)    and notebook PCs, are connected as terminals that are connected to    the recording server 100 through the network 500, receive image data    from the recording server 100 and display the data. In FIG. 1,    exemplary flows of image data captured on the recording PC are    depicted by dotted arrows. Note that in the following, the mobile    terminals and the browsing PCs are collectively referred to as    “terminals” or “Viewers”.

The recording server 100 is connected to the recording PCs 400B to 400Dthat are monitor targets through the network 500 including the Internet.In the embodiment, monitor target recording PCs can be provided onnetworks other than the LAN to which the recording server 100 isconnected as the recording PCs 400A, 400E, and 400F. To the Internetnetwork connected to the LAN to which the recording server 100 isconnected through a router 600A, 3G/LTE circuits are connected, andanother LAN is connected through a router 600C. The recording PC 400B isconnected to the Internet network through the router 600B through the3G/LTE circuit. The recording PCs 400C and 400D are connected the LAN towhich the recording server 100 is not connected. FIG. 1 shows anon-limiting exemplary connection in which the recording PCs, thebrowsing PCs, or the mobile terminals are connected to the recordingserver through a plurality of networks. In the embodiment,communications between the recording PC 400 and the recording server 100are performed in accordance with the Transport Control Protocol (TCP) ofhigh reliability in which a session is established and thencommunications are started.

Not only the recording PC as well as the browsing PC 300 that is animage display terminal are not limited to the case in which the PC 300is present in the LAN to which the recording server 100 is connected.The PC 300 may be connected to the recording server 100 through aplurality of networks, such as the Internet, LANs, and Wi-Fi circuits.The mobile terminal 200 that is an image display terminal may beconnected to the recording server 100 through a plurality of networks,such as LANs, the Internet, and mobile telephone networks (Wi-Ficircuits, 3G/LTE circuits, and any other circuits), for example. Notethat the router 600 is present between the LAN and the Internet andbetween the recording PC and the Internet.

One recording server 100 can sequentially acquire screen imagesdisplayed on a display 403 of the recording PC 400 from the plurality ofrecording PCs 400. In the embodiment, since image data is transferredfrom the recording PC 400 side to the recording server 100 at apredetermined timing, the recording server fails to grasp the situationswhen communications are disconnected. However, the load on networktraffic is small because information volumes to be transferred aresmall, and the ports of the routers do not have to be changed.

Note that in the embodiment, upon being activated, the recording PCauthenticates the connection to the recording server, and notifies therecording server that the recording PC is in the activated state. Afterthe recording server instructs the recording PC to start recording bythe acknowledge to the authentication, the recording PC acquires ascreen image, and then the recording PC acquires screen images at apredetermined interval using the timer of the recording PC. In theembodiment, images are acquired every certain time interval, at timingevery second or five seconds, for example, using the timer in therecording PC. A JPEG compressed full-screen image is created only at thefirst compression, and JPEG-compressed difference images are createdafter the first. The acquisition and compression are repeated until alapse of a predetermined recording time period, ten minutes, forexample, the compressed full-screen image and the compressed differenceimages in a predetermined recording time period are combined into afile, and the file is transferred to the recording server. Theseprocesses are repeated. In the compression of images into JPEG formats,zero degradation of image quality is enabled. An increase in JPEGcompression ratios is also enabled in the range visible to the humaneye.

In PC screen monitoring systems using conventional screen image transfermethods, volumes are large, compression processes are separately needed,or image quality is degraded. However, in the embodiment, the imagequality of the screen image on the display of the personal computer canbe prevented from being degraded, the screen image can be efficientlytransferred, and a decrease in the load of the PC processing data isenabled. Thus, volumes are sufficiently small, the recording PCs thatare monitor targets and portable terminals, for example, can be providedon the Internet as well as on the 3G/LTE circuits, and hence the degreeof freedom is considerably enhanced.

FIG. 2 is a block diagram of the recording PC of the first embodiment ofthe screen image transfer method according to the exemplary embodiment.The recording PC 400 is equipped with: a control arithmetic logic unithaving a central processing unit (CPU) 401 with a memory 402 that is acache memory, device drivers, and any other device; a storage device 410having a main storage device, such as a DRAM, and an auxiliary storagedevice, such as a hard disk; and an input-output device composed of acommunication controller, such as a network interface 404, the display403 that is a display device, a keyboard 405, a mouse 406, and any otherdevice. On the storage device 410, an accumulation folder 411, aconfiguration folder, a program 413, and an operating system 414 arestored. The program 413 is generally stored on the auxiliary storagedevice of the storage device 410, and is loaded to main storage devicein execution.

The accumulation folder 411 is a folder in which images are saved. Theaccumulation folder 411 accumulates compressed full-screen images andimage collections. The full-screen images are images that the completeimage of the full screen is acquired by capturing the screen shot of thedisplay 403 of the recording PC and then the images are JPEG-compressed.The image collections are created by the difference between a previouslycaptured complete image and a subsequently captured complete image. Inthe configuration folder, an image collection creation condition, acapture interval condition, a recording time period condition, acompression ratio condition, and any other condition are accumulated.

The program 413 includes various programs, such as an image recordingand transmission program. Upon receiving an image request from therecording server 100, the recording PC 400 performs a connectionauthentication process (activation). The server 100 and the PC 400 holdencryption keys and any other tools each other with such authenticationfor establishing connection. When the encryption keys and any othertools are different, the server 100 and the PC 400 fail to establishconnection. Thus, this can prevent information on the recording PC fromleaking to a server that is not involved.

In the embodiment, upon being activated, the recording PC 400 startsauthentication of the connection to the recording server, and thisnotifies the recording server that the recording PC is in the activatedstate. After the recording server 100 instructs the PC 400, first, therecording PC 400 performs the first-time screen image acquisition. Afterthat, the PC 400 acquires a screen image every certain interval usingthe timer of the recording PC, creates a predetermined file, andtransmits the file to the recording server 100.

The recording PC 400 achieves the function of a computer that enablesacquiring, editing and saving images and transmitting the images to therecording server in the monitoring method using the screen imagetransfer method according to the embodiment by the CPU 401 that loadsand executes the image recording and transmission program 413 on thememory 402. The CPU 401 is an arithmetic processing unit installed on atypical computer. The CPU 401 executes various programs, and performsvarious kinds of control, for example.

In the embodiment, the image recording and transmission program 413 is aprogram that causes a computer to achieve: (1) a connection functionthat receives a connection request from the recording server connectedvia the network for connection to the recording PC; (2) a full-screenimage acquiring function that acquires full-screen image data displayedon the screen of the display every certain time interval; (3) acompressed full-screen image creating function in which a full-screenimage acquired by the full-screen image acquiring function everypredetermined recording time period is JPEG-compressed to create andaccumulate a compressed full-screen image, a compressed full-screenimage is not created until a lapse of a predetermined recording timeperiod every time when a compressed full-screen image is created, andthe step goes to a subsequent step; (4) a splitting function that splitsthe full-screen image data acquired by the full-screen image acquiringfunction into block images with a predetermined matrix of pictureelements from one end of a screen area; (5) a positional informationcreating function that compares block images at two sequential timeinstants in every block image split by the splitting function to createpositional information data expressing the presence or absence of adifference and positional information about a block considered to have adifference according to how many blocks with a difference aresequentially arrayed and how many blocks with no difference aresequentially arrayed; (6) a parallel number calculating function thatcategorizes a block considered to have a difference determined by thepositional information creating function into a difference block, andcalculates, from the number of difference blocks at an identical timeinstant, the number of parallel blocks to be horizontally arranged inorder to form a rectangle with the smallest margin by arranging allblock images of the difference blocks at the identical time instant; (7)a compressed difference image creating function that repeats the step inwhich the block images of the difference blocks in the number of theparallel blocks calculated by the parallel number calculating functionare horizontally arranged and then arranged on the under side, createsan image collection in a rectangle with the margin blanked,JPEG-compresses the collection as one image, and creates and accumulatesthe compressed difference image; (8) a repeating function that repeatsthe steps from full-screen image acquisition to compressed differenceimage creation until a lapse of a predetermined recording time period;and (9) an accumulated image transferring function that creates anaccumulation data file including the compressed full-screen image, thecompressed difference images accumulated until a lapse of apredetermined recording time period, and pieces of positionalinformation data and transfers the file to the server.

The above-described certain interval time can be one second and fiveseconds, for example. A predetermined recording time period can be tenminutes, for example. Therefore, the compressed full-screen image (Iframe) is created in starting a predetermined recording time period,every ten minutes, for example, and the image that is created everycertain time period, one second, for example, during the ten minutes, isthe compressed difference image (the J frame). In the embodiment, theaccumulation data file is created as one file including an image thatcombines images for a predetermined recording time period, i.e. onecompressed full-screen image, a large number of compressed differenceimages, and positional information data. Note that the accumulation datafile is additionally provided with necessary information, such as aheader.

In the embodiment, in the splitting function, the block image is a blockof a matrix of eight by eight picture elements. The block image is theminimum unit in the JPEG format, and hence this combines the minimuminformation volume and maintaining resolution.

Note that in the embodiment, as an example, the block image is sized ina matrix of eight by eight picture elements. However, the size isnon-limiting. The size may be predetermined sizes (e.g. a 16 by 16picture element block). In the case in which a full-screen image issplit in a predetermined size unit, in creating the compressedfull-screen image and the compressed difference image, the images may beJPEG-compressed. However, images are preferably compressed in the blockunit that in the predetermined size. Thus, images can be compressed inthe block image unit for the difference block in creating the compresseddifference image, and hence when the block images of the differenceblocks is placed as it is in reconstructing the original full-screenimage, the original full-screen image can be correctly reproduced withno further processing.

Note that the method is non-limiting. In creating the compressedfull-screen image and the compressed difference image, images may becompressed in another image format, or images may be compressed byanother compressing method.

In the embodiment, the positional information creating function createsthe hash values of the block images and compared, and determines thatthe a block with an unequal calculated value is categorized into a blockwith a difference, and a block with an equal calculated value iscategorized into a block with no difference. The positional informationdata is one byte data or two byte data in which the presence or absenceof a difference is expressed by the first one bit and the number ofcontinuous blocks in which the presence or absence of difference is thesame is expressed by seven bits or 15 bits. In the case of one byte, thesequential number can be expressed up to 127. In the case two bytes, thesequential number can be expressed up to 32,767.

In regenerating the hash values of the block images for comparison, a 64bit hash value (1) is generated for the previously acquired image in aneight by eight matrix of picture elements (dots or pixels).Subsequently, a 64 bit hash value (2) is generated for the imageacquired this time in an eight by eight matrix of picture elements (dotsor pixels). In comparison of the hash value (1) with the hash value (2),when these values are equal, it is determined that no difference(change) is present, whereas in the case in which these values aredifferent in comparison of the hash value (1) with the hash value (2),it is determined that a difference (change) is present.

FIG. 3 is a conceptual diagram of when the difference image on therecording PC is created in the first embodiment of the screen imagetransfer method according to the exemplary embodiment. An image (imageA) previously acquired and an image acquired this time (image B) aresplit into blocks in a matrix of eight by eight picture elements, andthen only blocks with different images in the blocks at the samepositions between the image A and the image B (difference blocks) aresequentially arranged. When the blocks are arranged, all the blocks arearranged to form a rectangle with a margin. In order to form therectangle, the number of parallel blocks to be horizontally arranged iscalculated. In the embodiment, a predetermined number of pictureelements, eight picture elements, is advanced to the under side toarrange the blocks every time when the block images of the differenceblocks in the calculated number of the parallel blocks is horizontallyarranged. That is, the blocks are repeatedly arranged on the under sideevery calculated number of the parallel blocks, an image collection in arectangle with the margin blanked is created, the collection isJPEG-compressed as one image, and then the compressed difference imageis created. The repeat of the processes described above is a repeat ofprocesses in which the block images of the difference blocks in thecalculated number of the parallel blocks is horizontally arranged, andafter arranged, the block images of the difference blocks in the numberof the parallel blocks are horizontally arranged on the under side. Forexample, in the case in which the number of difference blocks at time t1is 11, a matrix of the blocks is composed of three by four blocks inorder to form a rectangle with the smallest margin. Thus, the firstblock to the fourth block are sequentially arranged on the first rowfrom the left, the fifth block to the eighth block are arranged on thesecond row below the first row, and then the ninth block to the eleventhblock are sequentially arranged on the third row from the left. Theright block on the third row is a with the margin blanked. Therefore,one image collection formed of a matrix of 24 by 32 picture elementswith difference blocks and an empty block is JPEG-compressed as oneimage. The JPEG minimum unit that is a matrix of eight by eight pictureelements is used, and hence when the compressed difference image isdivided into the individual difference block images, original differenceblock images can be obtained with no influence from the adjacent blocks.

Even though the original difference blocks are obtained, the originalimage is not formed unless the positions of the blocks are unknown.Thus, in transferring image collections to the recording server, theimage collections are each additionally provided with positionalinformation about each difference block. For example, in one byte, inthe case in which no difference (change) is present sequentially in 120blocks and a difference (change) is sequentially present in 300 blocks,the block considered to have a difference is expressed by one, the blockwith no difference is expressed by zero, and positional information isexpressed by 0:120 and 1:300. In bit expression where the presence orabsence of a difference is the first bit, 01111000 (the first positionalinformation: no change (0) in 120 blocks), 11111111 (the secondpositional information: changed (1) in 127 blocks), 11111111 (the thirdpositional information: changed (1) in 127 blocks), and 10101110 (thefourth positional information: changed (1) in 46 blocks (=300−127−127)).In two bytes, the manageable number of blocks can be increased.

The connection between the recording PC and the recording server isestablished in accordance with the Transmission ControlProtocol/Internet Protocol (TCP/IP). In order to identify the recordingPC, authentication is made using a user ID and a password set on therecording server side, and then a request is made to capture cameraimages, for example. Authentication is preferably made using anauthentication database on the recording server.

Even though the recording server does not belong to the LAN to which therecording PC is connected, when the server is connected via a networkthrough the router, the recording PC connects to the IP address and portnumber of the recording server.

FIG. 4 is a block diagram of the recording server of the firstembodiment of the screen image transfer method according to theexemplary embodiment. The recording server 100 is equipped with: acontrol arithmetic logic unit having a central processing unit (CPU) 101with a memory 102 that is a cache memory, device drivers, and any otherdevice; a storage device 110 having a main storage device, such as aDRAM, and an auxiliary storage device, such as a hard disk; and aninput-output device composed of a communication controller, such as anetwork interface 104, a display 103 that is a display device, akeyboard 105, a mouse 106, and any other device. On the storage device110, an accumulation folder 111, a primary picture folder 115, asecondary picture folder 112, a program 113, an authentication database,and a configuration folder, for example, as well as an operating system114 are stored. The program 113 is generally stored on the auxiliarystorage device of the storage device 110, and loaded to main storagedevice in execution.

The accumulation folder 111 is a folder that saves images. In theaccumulation folder 111, accumulation data files including thecompressed full-screen images and the compressed difference imagesacquired from the recording PC 400 are accumulated. In the primarypicture folder 115, moving images formed only of complete imagescomposed of the full-screen images reconstructed from the compressedfull-screen images and the compressed difference images accumulated inthe accumulation folder 111, i.e. moving images entirely composed of Iframes are accumulated as primary picture data. In the secondary picturefolder, primary picture data for a certain time period accumulated inthe primary picture folder 115 is moving image-compressed and converted,and accumulated as secondary picture data.

In the method of reconstructing a full-screen image from compresseddifference images, for example, in the case in which the image B in FIG.3 is reconstructed, regarding the number of blocks with no change (120blocks), block images are formed from the upper left block in theprevious image (in FIG. 3, the image A) in the same number (120 blocks)based on the first positional information (01111000) added to the imagecollection. Subsequently, regarding the number of blocks with changes(300 blocks), block images are sequentially formed in the same number(300 blocks) from the upper left block in the image collection based onthe second to the fourth positional information (11111111, 11111111, and10101110). Subsequently, regarding the number of blocks with no change(the number is supposed to be 100 blocks), block images in the samenumber (100 blocks) are formed from the 421st block image in the imageAbased on one piece or a plurality of pieces of positional informationat the fifth positional information and later that the first bit iszero. Regarding the number of blocks with changes (the number issupposed to be 50 blocks), block images are formed in the same number(50 blocks) from the 301st block image from the upper left block in theimage collection based on one piece or a plurality of sequential piecesof positional information. These processes are repeated to reconstructthe image B. Unlike camera images in natural environments in which lightfluctuates and winds blow, for example, on the PC screen, areas withchanges on the screen are often small, and hence the volume of the imagecollection can be considerably a small volume.

FIG. 5 is an illustration of a transfer method from the recording PC tothe recording server and a saving method on the recording server in aflow of the first embodiment of the screen image transfer methodaccording to the exemplary embodiment. In FIG. 5, the compressedfull-screen images are expressed as I frames, and compressed differenceimages are expressed as J frames. In converting and compressing a movingimage into secondary picture data, the number of I frames is decreased.The recording time period in which data is combined in one file andtransferred the file is ten minutes, for example, the number of I framesis decreased to about three frames per ten minutes, the numbers of Pframes and B frames are increased and inserted, and volumes are reducedwith no degradation. In this case, the number of J frames to betransferred from the recording PC to the recording server is 599 framesper ten minutes because the J frame is captured at the interval of everysecond. Since primary picture data is all composed of I frames, thenumber of I frames reaches 600 frames for a ten minute recording timeperiod. In secondary picture data, frames can be compressed as three Iframes, 197 P frames, and 400 B frames, for example, for a ten minuterecording time period.

The program 113 includes various programs, such as a gathering andediting program and a transmission program. In the authenticationdatabase, IDs and passwords are accumulated, and the connectionterminals, such as the screen PCs 400 and 701, the mobile terminal 200,and the browsing PC 300 are accumulated as unique identifications(UIDs). In the embodiment, the recording server 100 possesses therecording server and the terminal that are integrally formed. Since theserver 100 also serves as a function of an image display terminal byitself, the server 100 has the display 103, and the keyboard 105 and themouse 106 that are input units for maintenance and management. In thecase in which the replay of images of the recording PC is unnecessary inthe recording server, the terminal function as an image display devicemay not be provided. In the configuration folder, authenticationconditions with the recording PCs, the creation intervals of primarypicture data or secondary picture data, compression conditions, and anyother parameter are accumulated. Although the recording server 100 is aninstalled server, the server 100 may be a cloud server.

The recording PC 400 is connected to the recording server 100, andtransmits images in the case in which images are requested from theacknowledge of the communication. The timer of the recording PC is setat intervals of image transmission (one second, five seconds, and tenminutes, for example).

The recording server 100 achieves the functions of a computer thatenables processes from image acquisition from the recording PC to editand save of the image in the PC screen monitoring method using thescreen image transfer method according to the embodiment by loading thegathering and editing program to the memory 102 and executing theprogram by the CPU 101. The recording server 100 achieves the functionsof a computer that achieves the function of a computer that enables aprocess of transmission of the image to the terminal by loading thetransmitting program to the memory 102 and executing the program by theCPU 101. The CPU 101 is an arithmetic processing unit installed on atypical computer. The CPU 101 executes various programs, and performsvarious kinds of control, for example.

The recording server 100 is one server, or may be a server groupcomposed of a plurality of recording servers. For example, for thesecondary picture folder, secondary picture data after a lapse of acertain period (e.g. 24 hours) may be saved on a secondary picturefolder provided on another recording server different from the recordingserver that acquires compressed full-screen images and compresseddifference images. The data saved in the past that is not frequentlyreplayed is separated, and hence this enables monitoring of a largernumber of recording PCs on the same network.

The gathering and editing program is a program that causes a computer toachieve: (1) the recording PC connection function that connects therecording PC; (2) an image acquiring function that causes the recordingserver to receive the accumulation data file transferred from theconnected recording PC; (3) an accumulating function that accumulatesthe accumulation data file acquired from the recording PC in theaccumulation folder; (4) a difference block reconstructing function thatreconstructs an image collection from the compressed difference imagesincluded in the accumulated accumulation data file and reconstructs ablock image of difference blocks; (5) a full-screen image reconstructingfunction that places the block images of the difference blocks on thefull-screen image at the previous time instant based on the positionalinformation data and creates a full-screen image at the subsequent timeinstant on all the compressed difference images; and (6) a primarypicture data saving function that creates primary picture data as onemoving image in the accumulation data file unit from a collection of thereconstructed full-screen images and saves the data in a primary picturedata folder.

In the embodiment, the gathering and editing program, as a morepreferable aspect, is a program that also causes a computer to achieve asecondary picture data creating function that joins primary picture dataevery certain time period (e.g. ten minutes) and converts the primarypicture data into secondary picture data compressed in a moving imageformat with a time stamp, i.e. obtained by optimizing the primarypicture data. All pieces of the primary image data are complete images(I frames (intra-coded frames)). In the secondary picture data, primarypicture data is compressed in the moving image format. For example, thenumber of I frames is about three frames per ten minutes, a P frame(predictive inter frame) as well as a B frame (bidirectional predictiveinter frame) may be inserted in combination, which reduces the volumewith no degradation. In the embodiment, since reference can be made to aforward I frame, the B frame can be inserted. Since the B frame is thedifference between the current frame and the preceding and followingframes, the B frame is smaller than the P frame.

In the embodiment, a transmitting program is a program that causes acomputer to achieve: a terminal connecting function that connects theterminal; an image selection accepting function that displays arecording PC list on the terminal and accepts a selection of a recordingPC from the terminal; a replay image transmitting function thattransmits the image of secondary picture data of the selected recordingPC to the terminal; a replay-image-rewind-and-fast-forward acceptingfunction that accepts a replay image rewind request and a replay imagefast forward request from the terminal; and a rewound/fast-forwardedimage transmitting function that extracts secondary picture data at apoint in time by a certain time period (e.g. one second) in the past orin future from the image previously transmitted to the terminal for eachrewind request and each fast forward request and transmits the data as arewound image or a fast-forwarded image to the terminal. Note thatsimilarly to secondary picture data, the image of primary picture datacan also be transmitted to the terminal to replay, rewind, andfast-forward the image.

In the embodiment, the connection between the terminals 200 and 300 andthe recording server 100 is also performed in accordance with the TCP/IPmethod in which authentication is made using a user ID and a password,the terminal is confirmed that the terminal is registered on therecording server, and then the images are transmitted. Authentication ispreferably authentication by an authentication database on the recordingserver.

Even though the recording server does not belong to the LAN to which theterminal is connected, when the server is connected via a networkthrough the router, the terminal connects to the IP address and portnumber of the recording server. For the connection of the terminal, theterminal is authenticated using the UID registered in terminalauthentication.

Since the recording server 100 identifies the terminal based on terminalunique information using the UID in stating connection of the mobileterminal 200, the server 100 enables image display in accordance withauthentication of the user ID and the password and the matching ofterminal unique information.

FIG. 6 is a block diagram of the terminal (mobile terminal) of the firstembodiment of the screen image transfer method according to theexemplary embodiment. The mobile terminal 200 is equipped with: acontrol arithmetic logic unit having a CPU 201 with a memory 202, devicedrivers, and any other device; the storage device 210; a communicationcontroller that performs data transmission and reception, for example; adisplay 203 that is a display device; and an input-output device, suchas a manipulation button or a touch panel. On the storage device 210, animage display program 213 and an operating system 214 are stored. Forexample, the mobile terminal 200 is a mobile telephone, such as asmartphone. The terminal 200 achieves the functions of a computer thatenables image display in the monitoring method according to theembodiment by loading the image display program 213 to the memory 202and executing the program 213 by the CPU 201. The CPU 201 is anarithmetic processing unit installed on a typical mobile terminal, andthe CPU 201 executes various programs, and performs various kinds ofcontrol, for example.

FIG. 7 is a block diagram of the terminal (PC) of the first embodimentof the screen image transfer method according to the exemplaryembodiment. The browsing PC 300 is equipped with: a control arithmeticlogic unit having a CPU 301 with a memory 302, device drivers, and anyother device; a storage device 310 having a main storage device, such asa DRAM, and an auxiliary storage device, such as a hard disk; acommunication controller, such as a network interface 304; a display 303that is a display device; and an input-output device composed of akeyboard 305, a mouse 306, and any other device. On the storage device310, an image display program 313 and an operating system 314 arestored. The browsing PC 300 is a desktop PC, a notebook PC, a tabletterminal, and any other device, for example. The browsing PC 300achieves the functions of a computer that enables image displayaccording to the exemplary embodiment by loading the image displayprogram 313 on the memory 302 and executing the program 313 by the CPU301. The CPU 301 is an arithmetic processing unit installed on a typicalPC, and the CPU 301 executes various programs, and performs variouskinds of control, for example.

The image display program is a program that causes a computer to achievea terminal connecting function that establishes connection to therecording server, and an image display function that displays imagestransmitted from the recording server.

The image display program, as a more preferable aspect, is a programthat also causes a computer to achieve:

-   a rewind start requesting function that accepts an input of a rewind    request and requests the recording server for a rewound image during    replay image display; a rewind continuation requesting function that    requests the recording server for a rewound image every certain time    period (e.g. 0.2 second) shorter than an interval to request a    replay image during rewound image display; a rewound image fast    forward start requesting function that accepts an input of a fast    forward request from a user and requests the recording server for a    fast-forwarded image during rewound image display; and a rewound    image fast forward continuation requesting function that requests    the recording server for a fast-forwarded image every certain time    period (e.g. 0.2 seconds) shorter than an interval to request a    replay image during fast-forwarded image display.

In the embodiment, the recording server 100, the browsing PC 300, andthe recording PC 400 are all configured as a personal computer, and areequipped with a clock function and any other function that a typicalpersonal computer has. The mobile terminal 200 is also equipped with aclock function and any other function.

The recording PC 400 according to the first embodiment is a personalcomputer connected to the recording server 100 via the network, and thePC 400 is provided with: (1) a connecting unit that receives aconnection request from the recording server 100 to the recording PC;(2) a full-screen image acquiring unit that acquires full-screen imagedata displayed on the screen of the display 403 every certain timeinterval; (3) a compressed full-screen image creating unit in which thefull-screen image acquired by the full-screen image acquiring unit everypredetermined recording time period is JPEG-compressed to create andaccumulate a compressed full-screen image, a compressed full-screenimage is not created until a lapse of a predetermined recording timeperiod every time when a compressed full-screen image is created, andthe step goes to a subsequent step; (4) a splitting unit that splits thefull-screen image data acquired by the full-screen image acquiring unitinto block images with a predetermined matrix of picture elements fromone end of a screen area; (5) a positional information creating unitthat compares block images at two sequential time instants in everyblock image split by the splitting unit and creates positionalinformation data expressing presence or absence of a difference andpositional information about a block considered to have a differencebased on a block sequential number; (6) a parallel number calculatingunit that categorizes a block considered to have a difference determinedby the positional information creating unit into a difference block, andcalculates, from the number of difference blocks at an identical timeinstant, the number of parallel blocks to be horizontally arranged inorder to form a rectangle with the smallest margin by arranging allblock images of the difference blocks at the identical time instant; (7)a compressed difference image creating unit that repeats a step in whichthe block images of the difference blocks in the number of the parallelblocks calculated by the parallel number calculating unit arehorizontally arranged and then arranged on the under side, creates animage collection in a rectangle with the margin blanked, JPEG-compressesthe collection as one image, and creates and accumulates the compresseddifference image; (8) a repeating unit that repeats the steps fromfull-screen image acquisition to compressed difference image creationuntil a lapse of a predetermined recording time period; and (9) anaccumulated image transferring unit that creates an accumulation datafile including the compressed full-screen image, the compresseddifference images accumulated until a lapse of a predetermined recordingtime period, and pieces of positional information data and transfers thefile to the server.

The recording PC 400 functions as the units (1) to (9) with the hardwareconfiguration and the image recording and transmission program describeabove.

The recording server 100 according to the first embodiment is providedwith: (1) a recording PC connecting unit that connects the recording PC;(2) an image acquiring unit that causes the recording server 100 toreceive an accumulation data file transferred from the connectedrecording PC; (3) an accumulating unit that accumulates the accumulationdata file acquired from the recording PC 400 in the accumulation folder111; (4) a difference block reconstructing unit that reconstructs animage collection from the compressed difference images included in theaccumulated accumulation data file and reconstructs a block image ofdifference blocks; (5) a full-screen image reconstructing unit thatplaces the block images of the difference blocks on the full-screenimage at the previous time instant based on the positional informationdata and creates a full-screen image at the subsequent time instant onall the compressed difference images; and (6) a primary picture datasaving unit that creates primary picture data as one moving image in theaccumulation data file unit from a collection of the reconstructedfull-screen images the primary picture data folder 115.

The recording server 100 functions as the units (1) to (6) with thehardware configuration and the gathering and editing program describedabove. The recording server 100 functions as a transmitting unit thattransmits replay images, rewound replay images, fast forward replayimages to the terminal with the hardware configuration and thetransmitting program described above.

The terminals 200 and 300 are provided with:

-   (1) a recording server connecting unit that connects the recording    server 100; (2) an image display unit that displays images    transmitted from the recording server 100; (3) a rewind start    requesting unit that accepts an input of a rewind request and    requests the recording server for a rewound image during replay    image display; (4) a rewind continuation request unit that requests    the recording server for a rewound image every certain time period    (e.g. 0.2 seconds) shorter than an interval to request a replay    image during rewound image display; (5) a rewound image fast forward    start requesting unit that accepts an input of a fast forward    request from a user and requests the recording server for a    fast-forwarded image during rewound image display; and (6) a rewound    image fast forward continuation request unit that requests the    recording server for a fast-forwarded image every certain time    period (e.g. 0.2 seconds) shorter than an interval to request a    replay image during fast-forwarded image display. The terminal    functions as the units (1) to (6) with the hardware configuration    and the image display programs 213 and 313 described above.

Note that since primary picture data created using only complete images(I frames) is converted into secondary picture data at the recordingserver every certain time period, the terminal enables the replay,rewind replay, and fast forward replay of images in a short time, suchas a lapse of ten minutes after images are recorded, and also enablesthe replay, rewind, and fast forward of past screen images of therecording PC after a lapse of a day or longer. Although data volumes aresmall in the transmission of data from the recording PC to the recordingserver, replay images, rewound images, and fast-forwarded images are allI frames, and hence the images are of high image quality when replayedas moving images. When past images are replayed, fast forwarded, orrewound in a secondary data creating unit or more, which is notfrequently used, secondary picture data that is a compressed andconverted moving image file is used, and hence the data volume necessaryfor saving is small although the data is a moving image.

The PC screen monitoring system composed of the recording PC, therecording server, and the terminal described above is a system thatachieves the screen image transfer method according to the firstembodiment and the image reconstructing method according to the firstembodiment. The system detects differences of the PC screens in JPEGunits, generates another image with these differences, and transfersimages, and hence volumes to be transferred can be reduced. A monitoringsystem can be achieved in which loads on the recording PC thatcompresses images are also small, data volumes to be transmitted fromthe recording PC to the recording server are small, a problem, such asdata delay, is not prone to occur even though the recording PC isprovided in environments other than local environments, data volumes tobe transmitted from the recording server to the terminal is also small,and loads on the network are small while the system is of highresolution and high image quality. That is, the image quality of thescreen image on the display of the personal computer can be preventedfrom being degraded, the screen image can be efficiently transferred,and a decrease in the load of the PC processing data is enabled. Datavolumes simultaneously flowing on the network are small, and hence PCscreen images can be flowed to the recording server via general Internetcircuits, for example, and PC screen information can also be flowed togeneral Internet circuits, for example. Data accumulation is enabledusing a cloud server over the Internet circuit (wide area network(WAN)).

{Procedures}

The procedures of the first embodiment of the screen image transfermethod according to the exemplary embodiment will be described more indetail with reference to the drawing. In the procedures, the PC screenmonitoring system composed of the recording PC, the recording server,and the terminal described above is used.

FIG. 8 is a flowchart showing the outline of procedures from capturingthe screen of the recording PC to accumulation on the recording serverin the first embodiment of the screen image transfer method according tothe exemplary embodiment.

The recording PC requests the recording server for connection inaccordance with the TCP/IP method. The recording PC is composed of oneor a plurality of recording PCs. The recording PC makes authenticationwith the recording server using the user ID and the password. Uponreceiving a connection acknowledge from the recording PC, the recordingserver successfully achieves authentication with reference to theauthentication database, the recording server is in connection with therecording PC.

In the screen image transfer method according to the embodiment, afterthe recording PC is in the activated state, the recording PCauthenticates the connection to the recording server described above.After the recording server requests the recording PC to start recording,the recording PC acquires full-screen image data displayed on the screenof the display, JPEG-compresses the acquired full-screen image, createsa compressed full-screen image, and accumulates the image. Thecompressed full-screen image is created every predetermined recordingtime period, ten minutes, for example.

After creation of the compressed full-screen image, full-screen imagedata displayed on the screen of the display is acquired, and then thecompressed difference image is created every certain interval time (e.g.one second or five seconds). These processes are repeated until a lapseof a predetermined recording time period (e.g. ten minutes). Forexample, in the case in which the recording time period is ten minutes(600 seconds) and the interval time is one second, the first one is acompressed full-screen image and the number of compressed differenceimages is 599 images at the maximum. In the case in which no differenceis present, no image collection is available for that time instant, andhence no compressed difference image is present.

An accumulation data file including one compressed full-screen image,compressed difference images (in the case, 599 images at the maximum),and positional information data of each compressed difference imagedescribed above is created, and transferred to the recording server.

After a lapse of a predetermined recording time period, the recording PCacquires full-screen image data displayed on the screen of the display,creates and accumulates a compressed full-screen image, acquiresfull-screen image data displayed on the screen of the display everycertain time interval, creates and accumulates the compressed differenceimages, and then creates an accumulation data file, and transfers thefile to the recording server. These processes are repeated.

For creating a compressed difference image, the acquired full-screenimage data is split into block images with a predetermined matrix ofpicture elements from one end of a screen area, block images at twosequential time instants are compared in every split block image,positional information data expressing the presence or absence of adifference and positional information about a block considered to have adifference based on the sequential numbers of blocks is created, theblock considered to have a difference is categorized into a differenceblock, the number of parallel blocks to be horizontally arranged inorder to form a rectangle with the smallest margin by arranging allblock images of the difference blocks at the identical time instant iscalculated from the number of difference blocks at an identical timeinstant, the step is repeated in which the block images of thedifference blocks in the calculated number of the parallel blocks arehorizontally arranged and then arranged on the under side, an imagecollection in a rectangle with the margin blanked is created, thecollection is JPEG-compresses as one image, and then a compresseddifference image is created.

That is, the embodiment includes: (1) a full-screen image acquiring stepin which a personal computer connected to a server via a networkacquires full-screen image data displayed on the screen of a displayevery certain time interval; (2) a compressed full-screen image creatingstep in which full-screen images acquired in the full-screen imageacquiring step are JPEG-compressed every predetermined recording timeperiod to create and accumulate a compressed full-screen image, acompressed full-screen image is not created until a lapse of apredetermined recording time period every time when a compressedfull-screen image is created, and the step goes to a subsequent step;(3) a splitting step in which the full-screen image data acquired in thefull-screen image acquiring step is split into block images with apredetermined matrix of picture elements from one end of a screen area;(4) a positional information creating step in which block images at twosequential time instants are compared in every block image split in thesplitting step to create positional information data expressing presenceor absence of a difference and positional information about a blockconsidered to have a difference based on a block sequential number; (5)a parallel number calculating step in which a block determined as ablock considered to have a difference in the positional informationcreating step is categorized into a difference block to calculate, fromthe number of difference blocks at an identical time instant, the numberof parallel blocks to be horizontally arranged in order to form arectangle with the smallest margin by arranging all block images of thedifference blocks at the identical time instant; (6) a compresseddifference image creating step in which a step is repeated in which theblock images of the difference blocks in the number of the parallelblocks calculated in the parallel number calculating step arehorizontally arranged and then arranged on the under side, an imagecollection in a rectangle with the margin blanked is created, thecollection is JPEG-compressed as one image, and the compresseddifference image is created and accumulated; (7) repeating the steps (1)from (6) until a lapse of a predetermined recording time period; and (8)an accumulated image transferring step in which after that, theaccumulation data file including the compressed full-screen image, thecompressed difference images accumulated until a lapse of apredetermined recording time period, and pieces of positionalinformation data is created and the file is transferred to the server.The steps (1) from (8) are sequentially performed until the power supplyof the recording PC is turned off or until connection to the recordingserver is disconnected.

In the embodiment, in the splitting step, the block image is in a matrixof eight by eight picture elements. In the positional informationcreating step, in the comparison of block images at two sequential timeinstants with each other, a hash value is generated for the block imagesand compared, the block with an unequal calculated value is categorizedinto a block with a difference, and the block with an equal calculatedvalue is categorized into a block with no difference. The positionalinformation data is one byte data or two byte data in which the firstone bit expresses the presence or absence of a difference and seven bitsor 15 bits express the number of continuous blocks in which the presenceor absence of difference is the same.

In JPEG, an image is split into fixed-sized blocks of a matrix of eightby eight picture elements. The image is converted in the block unitsusing discrete cosine transform (DCT). The information volume isdecreased by quantization, and then the image is compressed. When atypical image in the format other than JPEG is quantized as it is, imagequality is greatly degraded. However, in JPEG compression, quantizationis enabled as the properties of the original image remain. That is, inJPEG, even any large-sized image is split into fixed-sized blocks, theimage is compressed in every block, and hence the blocks are notaffected even though totally different images are adjacent to each otherin the block units. In the embodiment, JPEG compression is used with theJPEG properties. In the embodiment, the processes from the extraction ofdifferences, compression, reconstruction, and expansion are based on theJPEG block size, and hence difference information is managed in theminimum volume, achieving the minimum load of the PC processing data.

The positional information may be coordinates management in addition tobit sequences. The image collection is JPEG-compressed as it is, and aJPEG image is generated, i.e. an image is compressed at high speed withthe minimum CPU load.

The program of the PC screen monitoring system having the imagerecording and transmission program causes a computer to execute thesesteps.

Upon acquiring images from the recording PC, the recording serverreconstructs the images. First, the recording server determines thepresence or absence of an accumulation data file. In the case in whichno accumulation data file is present, the recording server goes intosleep mode until a lapse of the recording time period, and repeats suchdetermination. In the case in which an accumulation data file ispresent, the recording server performs a difference block reconstructingstep in which the recording server reconstructs an image collection fromcompressed difference images and reconstructs the block images of thedifference blocks, and then performs a full-screen image reconstructingstep in which the recording server repeats placing the block images ofthe difference blocks on the full-screen image at the previous timeinstant based on the positional information data and creating afull-screen image at the subsequent time instant for a predeterminedrecording time period.

Since the reconstructed images are all full-screen images (I frames),the images are accumulated in the primary picture folder as primarypicture data of a moving image formed only of I frames in the recordingtime period unit. After that, the primary picture data is movingimage-compressed and secondary picture data is sometimes created, andthen the secondary picture data is accumulated in the secondary picturefolder. Specifically, secondary picture data is a compressed movingimage in the H.264 format including P frames and B frames with thenumber of I frames decreased.

The embodiment is the screen image transfer method that can be used forthe recording PC monitoring system for management, for example, withwhich captured PC screen images are transferred to the server, datatransferred to the recording server that accumulates data isreconstructed into images that can be displayed on the terminal by theimage reconstructing method described above. The difference blocks ofthe compressed difference images that have been JPEG-compressed are allplaced on the complete image at the previous time instant based on thebit sequences or the coordinates information. After all the differenceblocks are placed, the complete image at the subsequent time instant isobtained.

(Effect)

According to the embodiment, the image quality of the screen image onthe display of the personal computer can be prevented from beingdegraded, the screen image can be efficiently transferred, and adecrease in the load of the PC processing data is enabled.

The minimum image degradation is achieved, JPEG is adopted, images arecompressed, and hence another compression process is eliminated.Differences are converted into JPEG images as they are with no change inthe number of colors or data formats, and hence difference data can beautomatically created in the minimum time and a highly compressed statecan be achieved.

Second Embodiment

FIG. 9 is a flowchart showing the outline of procedures from capturingthe screen of a recording PC to accumulation on a recording server of asecond embodiment of the screen image transfer method according to theexemplary embodiment. In the screen image transfer method and the imagereconstructing method according to the second embodiment, points otherthan below are similar to those of the first embodiment described above.

In the embodiment, images combined in a predetermined recording timeperiod are not transferred from the recording PC to the recordingserver. A step is repeated. In the step, images are acquired at timingevery certain time interval, one second or five seconds, for example,using a timer in the recording PC. After the recording server sends animage request, a compressed full-screen image is created only at thefirst time, and then compressed difference images are created. After afull screen data file including the compressed full-screen image or adifference data file including the compressed difference image andpositional information data is created, these files are transferred tothe recording server, and the transferred image is deleted, and thenthese steps are repeated. Note that the full screen data file and thedifference data file are additionally provided with necessaryinformation, such as a header. The compressed full-screen image iscreated in starting a predetermined recording time period, and thecompressed difference image is created every certain time intervalduring creation of the compressed full-screen image. This is the same asin the first embodiment.

The embodiment includes: (1) a full-screen image acquiring step in whicha personal computer connected to a server via a network acquiresfull-screen image data displayed on the screen of a display everycertain time interval; (2) a compressed full-screen image creating stepin which full-screen images acquired in the full-screen image acquiringstep are JPEG-compressed every predetermined recording time period tocreate and accumulate a compressed full-screen image, a compressedfull-screen image is not created until a lapse of a predeterminedrecording time period every time when a compressed full-screen image iscreated, and the step goes to a subsequent step; (3) a full-screen imagetransferring step in which a full screen data file including thecompressed full-screen image created in the full-screen image creatingstep is created and the file is transferred to the server; (4) asplitting step in which the full-screen image data acquired in thefull-screen image acquiring step is split into block images with apredetermined matrix of picture elements from one end of a screen area;(5) a positional information creating step in which block images at twosequential time instants are compared in every block image split in thesplitting step to create positional information data expressing presenceor absence of a difference and positional information about a blockconsidered to have a difference based on a block sequential number; (6)a parallel number calculating step in which a block determined as ablock considered to have a difference in the positional informationcreating step is categorized into a difference block to calculate, fromthe number of difference blocks at an identical time instant, the numberof parallel blocks to be horizontally arranged in order to form arectangle with the smallest margin by arranging all block images of thedifference blocks at the identical time instant; (7) a compresseddifference image creating step in which a step is repeated in which theblock images of the difference blocks in the number of the parallelblocks calculated in the parallel number calculating step arehorizontally arranged and then arranged on the under side, an imagecollection in a rectangle with the margin blanked is created, thecollection is JPEG-compressed as one image, and the compresseddifference image is created and accumulated; and (8) a difference imagetransferring step in which a difference data file including thecompressed difference image and pieces of positional information data iscreated and the file is transferred to the server. The steps (1) from(8) are sequentially performed until the power supply of the recordingPC is turned off or until connection to the recording server isdisconnected.

In the embodiment, an image recording and transmission program 413 onthe recording PC is almost the same as the image recording andtransmission program of the screen image transfer method according tothe first embodiment. However, the program 413 is different from theprogram according to the first embodiment. The program 413 is a programthat causes a computer to also achieve: a full-screen image transferringfunction that creates a full screen data file including the compressedfull-screen image created by the full-screen image creating function andtransfers the file to the server; and a difference image transferringfunction that creates a difference data file including the compresseddifference image and pieces of positional information data and transfersthe file to the server, instead of the accumulated image transferringfunction.

A recording PC 400 according to the embodiment is almost the same as therecording PC in the screen image transfer method according to the firstembodiment. However, the recording PC 400 is different from therecording PC according to the first embodiment. The recording PC 400 isalso provided with: a full-screen image transferring unit that creates afull screen data file including the compressed full-screen image createdby the full-screen image creating unit and transfers the file to theserver; and a difference image transferring unit that creates adifference data file including the compressed difference image andpieces of positional information data and transfers the file to theserver, instead of the accumulated image transferring unit.

In the embodiment, the difference image of a still image on the screenof the recording PC is compressed by a predetermined method andtransferred. Thus, information volumes can be decreased at the minimum,volumes to be transferred from the recording PC to the recording servercan be made small, and gathering of the screen images of the recordingPC is enabled with no recording server installed at a local site. Datavolumes on communications can be decreased, compared with simplegathering of screen images of the recording PC, a load on the network issmall, as well as monitoring with images of high resolution is enabledwhen images are reconstructed. Note that a composite image transferringmethod may be formed in which the first embodiment described above thataccumulates images and then transfers images is combined with the secondembodiment described above that transfers differences in real time.

In the embodiment, a gathering and editing program of a recording server100 is a program that causes a computer to achieve: (1) a recording PCconnection function that connects the recording PC; (2) an imageacquiring function that causes the recording server to receive the fullscreen data file transferred from the connected recording PC and thedifference data file; (3) an accumulating function that accumulates thefull screen data file and the difference data file acquired from therecording PC on the accumulation folder; (4) a difference blockreconstructing function that reconstructs an image collection from eachof compressed difference images included in the accumulated differencedata file and reconstructs block images of the difference blocks; (5) afull-screen image reconstructing function that places the block imagesof the difference blocks on a full-screen image at the previous timeinstant based on positional information data and creates a full-screenimage at the subsequent time instant for all the compressed differenceimages; and (6) a primary picture data saving function that expands thereconstructed full-screen image on a memory, creates primary picturedata as one moving image in the predetermined recording unit from acollection of the reconstructed full-screen images, and saves the datain a primary picture data folder. In the embodiment, similarly to thefirst embodiment described above, the gathering and editing program is aprogram that also causes a computer to achieve a secondary picture datasaving function that optimizes primary picture data, creates secondarypicture data, and saves the data in a secondary picture data folder.

In an accumulation folder 111, a full screen data file including thecompressed full-screen image acquired from the recording PC 400 and adifference data file including compressed difference images areaccumulated. In a primary picture folder 115, moving images formed onlyof complete images composed of the full-screen images reconstructed fromthe compressed full-screen images and the compressed difference imagesaccumulated in the accumulation folder 111, i.e. moving images entirelycomposed of I frames are accumulated as primary picture data. Theprimary picture data is all single images (complete images), and henceprocesses are formed in replay in a considerably simple manner.According to the embodiment, data can be transmitted as moving images tothe monitoring-side terminal in real time, and convenience is high. Inthe secondary picture folder, primary picture data for a certain timeperiod accumulated in the primary picture folder 115 is movingimage-compressed and converted, and accumulated as secondary picturedata. In converting and compressing a moving image into secondarypicture data, the number of I frames is decreased, for example thenumber of I frames is decreased to about three frames per ten minutes,the numbers of P frames and B frames are increased and inserted, andvolumes are reduced with no degradation.

The PC screen monitoring system described above transmits imagesreconstructed by the image reconstructing method according to the firstembodiment to the terminal, for example, and the system replays,rewinds, and fast-forwards live images, and replays libraries as well.The PC screen monitoring system compresses and saves the reconstructedimages, transmits the images to the terminal, for example, and thesystem replays, rewinds, and fast-forwards past images as well. The term“library replay” here means replay after a live image is rewound to thepast or means the fast forward replay of images in the past.

In the embodiment, a transmitting program is a program that causes acomputer to achieve: a terminal connection function that connects theterminal; an image selection accepting function that displays arecording PC list on the terminal and accepts a selection of a recordingPC from the terminal; a live image transmitting function that transmitsthe image of primary picture data of the selected recording PC as a liveimage to the terminal; a live image rewind accepting function thataccepts a request to rewind the live image from the terminal; a rewoundlive image transmitting function that extracts primary picture data at apoint in time by a certain time period (e.g. one second) in the pastfrom the image previously transmitted to the terminal for each rewindrequest and transmits the extracted data as a rewound live image to theterminal; a rewound live image fast forward accepting function thataccepts a request for the fast forwarded rewound live image from theterminal; and a fast forwarded live image transmitting function thatextracts primary picture data at a point in time by a certain timeperiod (e.g. one second) in the future from the image previouslytransmitted to the terminal for each fast forward request until theimage at the present point in time is reached and transmits the data asa fast forwarded live image to the terminal. The term “image at thepresent point in time” means the newest image acquired from therecording PC. Therefore, the image at the present point in time ischanged to a new image every time when images from the recording PC areinputted to the recording server.

The transmitting program is a program that also causes a computer toachieve: a library image accepting function that accepts a request for alibrary image from a rewound live image from the terminal; and a libraryimage transmitting function that extracts primary image data at a pointin future time from the image previously transmitted to the terminal bya certain time period, i.e. by an interval for acquiring latest splitdata from the recording PC 400 to the recording server 100 for eachlibrary image request and transmits the data as a fast forwarded liveimage to the terminal. Note that the term “library image” stated heremeans a replayed image after a live image is rewound to the past.Replay, rewind, and fast forward using secondary picture data aresimilar to those of the first embodiment described above.

According to the embodiment, the image quality of the screen image onthe display of the personal computer can be prevented from beingdegraded, the screen image can be efficiently transferred, and adecrease in the load of the PC processing data is enabled. Althoughinformation volumes are increased more than in the first embodiment, thesecond embodiment is also suited to monitoring in real time.

Note that the exemplary embodiment is not limited to the embodiments,and various modifications are enabled in the scope not deviating fromthe gist of the exemplary embodiment. The components of the embodimentscan be freely combined in the scope not deviating from the gist of theexemplary embodiment.

The recording PCs in the embodiments may execute various processesdescribed above by a method with which the programs to execute processesby the recording PCs in the embodiments are recorded on a computerreadable recording medium to form an image compressing program product,the recording PC is caused to read the programs recorded on therecording medium, and the processor executes the programs.

The recording servers in the embodiments may execute various processesdescribed above by a method with which the programs to execute processesby the recording servers in the embodiments are recorded on a computerreadable recording medium to form an image reconstructing programproduct, the recording server is caused to read the programs recorded onthe recording medium, and the processor executes the programs.

What is claimed is:
 1. A screen image transfer method comprising: afull-screen image acquiring step in which a terminal device connected toan image reconstructing device via a network acquires full-screen imagedata displayed on a screen of a display every certain time interval; acompressed full-screen image creating step in which a full-screen imageacquired every predetermined recording time period in the full-screenimage acquiring step is compressed by a method of compressing thefull-screen image in every block in a set size to create and accumulatea compressed full-screen image, a compressed full-screen image is notcreated until a lapse of a predetermined recording time period everytime when a compressed full-screen image is created, and the step goesto a subsequent step; a full-screen image transferring step in which afull screen data file including the compressed full-screen image createdin the full-screen image creating step is created and the full screendata file is transferred to an image reconstructing device; a splittingstep in which the full-screen image data acquired in the full-screenimage acquiring step is split into block images in the set size; apositional information creating step in which block images at two timeinstants are compared in every block image split in the splitting stepto create positional information data expressing presence or absence ofa difference and positional information about a difference; a parallelnumber calculating step in which a block determined as a blockconsidered to have a difference in the positional information creatingstep is categorized into a difference block to calculate, from a numberof difference blocks at an identical time instant, a number of parallelblocks to be horizontally arranged in order to form a rectangle with thesmallest margin by arranging all block images of difference blocks at anidentical time instant; a compressed difference image creating step inwhich a step is repeated in which the block images of the differenceblocks in the number of parallel blocks calculated in the parallelnumber calculating step are horizontally arranged, and an imagecollection created in a rectangle with the margin blanked is compressedby a method with which the image collection is compressed as one imagein every block in the set size to create and accumulate a compresseddifference image; and a difference image transferring step in which adifference data file including the compressed difference image andpieces of positional information data is created and the difference datafile is transferred to an image reconstructing device.
 2. The screenimage transfer method according to claim 1, wherein in the positionalinformation creating step, in the comparison, a hash value is generatedfor each block image and compared, a block with an unequal calculatedvalue is categorized into a block with a difference, and a block with anequal calculated value is categorized into a block with no difference;and the positional information data is one byte data or two byte data inwhich a first one bit expresses presence or absence of a difference andseven bits or 15 bits express a number of continuous blocks in which thepresence or absence of difference is the same.
 3. The screen imagetransfer method according to claim 1, wherein: the steps from thefull-screen image acquiring step to the compressed difference imagecreating step are repeated until a lapse of the predetermined recordingtime period except the full-screen image transferring step; and afterthe steps, instead of the compressed difference image transferring step,the method includes an accumulated image transferring step in which anaccumulation data file including the compressed full-screen image, thecompressed difference images accumulated until a lapse of apredetermined recording time period, and pieces of positionalinformation data is created and the accumulation data file istransferred to an image reconstructing device.
 4. A reconstructingmethod for an image transferred to an image reconstructing deviceaccording to the screen image transfer method according to claim 1, thereconstructing method comprising: a difference block reconstructing stepin which the image collection is reconstructed from the compresseddifference image to reconstruct block images of difference blocks; and afull-screen image reconstructing step of repeating a step for thepredetermined recording time period in which the block image of thedifference block is placed on a full-screen image at a previous timeinstant based on the positional information data to create a full-screenimage at subsequent time instant.
 5. A screen image transfer systemcomprising: a full-screen image acquiring unit configured to acquirefull-screen image data displayed on a screen of a display every certaintime interval by a terminal device connected to an image reconstructingdevice via a network; a compressed full-screen image creating unitconfigured to compress the full-screen image acquired at the full-screenimage acquiring unit every predetermined recording time period by amethod with which the full-screen image is compressed in every block ina set size to create and accumulate a compressed full-screen image, inwhich a compressed full-screen image is not created until a lapse of apredetermined recording time period every time when a compressedfull-screen image is created, and the step goes to a subsequent step; afull-screen image transferring unit configured to create a full screendata file including the compressed full-screen image created at thefull-screen image creating unit and transfer the accumulation data fileto an image reconstructing device; a splitting unit configured to splitthe full-screen image data acquired at the full-screen image acquiringunit into block images in the set size; a positional informationcreating unit configured to compare block images at two time instants inevery block image split at the splitting unit to create positionalinformation data expressing presence or absence of a difference andpositional information about a difference; a parallel number calculatingunit configured to categorize a block determined as a block with adifference at the positional information creating unit into a differenceblock, and calculate, from a number of difference blocks at an identicaltime instant, a number of parallel blocks to be horizontally arranged inorder to form a rectangle with the smallest margin by arranging allblock images of difference blocks at an identical time instant; acompressed difference image creating unit configured to repeat a step inwhich the block images of the difference blocks in the number ofparallel blocks calculated at the parallel number calculating unit arehorizontally arranged, compress an image collection created in arectangle with the margin blanked by a method with which the imagecollection is compressed as one image in every block in the set size andcreate and accumulate a compressed difference image; and differenceimage transferring unit configured to create a difference data fileincluding the compressed difference image and pieces of positionalinformation data and transfer the difference data file to an imagereconstructing device.
 6. An image reconstructing system thatreconstructs an image transferred by the screen image transfer systemaccording to claim 5, the image reconstructing system comprising: adifference block reconstructing unit configured to reconstruct the imagecollection from the compressed difference image and reconstruct a blockimage of a difference block; and a full-screen image reconstructing unitconfigured to repeat a step for the predetermined recording time periodin which the block image of the difference block is placed on afull-screen image at previous time instant based on the positionalinformation data and a full-screen image at subsequent time instant iscreated.
 7. A recording medium recording a screen image transferringprogram that causes a computer to execute: a full-screen image acquiringstep in which a terminal device connected to an image reconstructingdevice via a network acquires full-screen image data displayed on ascreen of a display every certain time interval; a compressedfull-screen image creating step in which a full-screen image acquiredevery predetermined recording time period in the full-screen imageacquiring step is compressed by a method of compressing the full-screenimage in every block in a set size to create and accumulate a compressedfull-screen image, a compressed full-screen image is not created until alapse of a predetermined recording time period every time when acompressed full-screen image is created, and the step goes to asubsequent step; a full-screen image transferring step in which a fullscreen data file including the compressed full-screen image created inthe full-screen image creating step is created and the full screen datafile is transferred to an image reconstructing device; a splitting stepin which the full-screen image data acquired in the full-screen imageacquiring step is split into block images in the set size; a positionalinformation creating step in which block images at two time instants arecompared in every block image split in the splitting step to createpositional information data expressing presence or absence of adifference and positional information about a difference; a parallelnumber calculating step in which a block determined as a block with adifference in the positional information creating step is categorizedinto a difference block to calculate, from a number of difference blocksat an identical time instant, a number of parallel blocks to behorizontally arranged in order to form a rectangle with the smallestmargin by arranging all block images of difference blocks at anidentical time instant; a compressed difference image creating step inwhich a step is repeated in which the block images of the differenceblocks in the number of parallel blocks calculated in the parallelnumber calculating step are horizontally arranged, and an imagecollection created in a rectangle with the margin blanked is compressedby a method with which the image collection is compressed as one imagein every block in the set size to create and accumulate a compresseddifference image; and a difference image transferring step in which adifference data file including the compressed difference image andpieces of positional information data is created and the difference datafile is transferred to an image reconstructing device.
 8. A recordingmedium recording a reconstructing program for an image transferred to animage reconstructing device by execution of the screen imagetransferring program according to claim 7, the reconstructing programthat causes a computer to execute: a difference block reconstructingstep in which the image collection is reconstructed from the compresseddifference image to reconstruct a block image of a difference block; anda full-screen image reconstructing step of repeating a step for thepredetermined recording time period in which the block image of thedifference block is placed on a full-screen image at previous timeinstant based on the positional information data to create a full-screenimage at subsequent time instant.
 9. An image compressing methodcomprising: a parallel number calculating step in which block images attwo time instants are compared in every block image in which full-screenimage data displayed on a screen of a display is split, a block with adifference is categorized into a difference block, and a number ofparallel blocks to be horizontally arranged is calculated, from a numberof difference blocks at an identical time instant, in order to form arectangle with the smallest margin by arranging all block images ofdifference blocks at an identical time instant; and a compresseddifference image creating step in which a step is repeated in which theblock images of the difference blocks in the number of parallel blockscalculated in the parallel number calculating step are horizontallyarranged, and an image collection created in a rectangle with the marginblanked is compressed as one image to create a compressed differenceimage.
 10. An image compressing system comprising: a parallel numbercalculating unit configured to compare block images at two time instantsin every block image in which full-screen image data displayed on ascreen of a display is split, categorize a block with a difference intoa difference block, and calculate a number of parallel blocks to behorizontally arranged, from a number of difference blocks at anidentical time instant, in order to form a rectangle with the smallestmargin by arranging all block images of difference blocks at anidentical time instant; and a compressed difference image creating unitconfigured to repeat a step in which the block images of the differenceblocks in the number of parallel blocks calculated in the parallelnumber calculating step are horizontally arranged, and compress an imagecollection created in a rectangle with the margin blanked as one imageto create a compressed difference image.
 11. A recording mediumrecording an image compressing program that causes a computer toexecute: a parallel number calculating step in which block images at twotime instants are compared in every block image in which full-screenimage data displayed on a screen of a display is split, a block with adifference is categorized into a difference block, and a number ofparallel blocks to be horizontally arranged is calculated, from a numberof difference blocks at an identical time instant, in order to form arectangle with the smallest margin by arranging all block images ofdifference blocks at an identical time instant; and a compresseddifference image creating step in which a step is repeated in which theblock images of the difference blocks in the number of parallel blockscalculated in the parallel number calculating step are horizontallyarranged, and an image collection created in a rectangle with the marginblanked is compressed as one image to create a compressed differenceimage.
 12. A screen image transfer method comprising: a full-screenimage acquiring step in which a personal computer connected to a servervia a network acquires full-screen image data displayed on screen of adisplay every certain time interval; a compressed full-screen imagecreating step in which a full-screen image acquired every predeterminedrecording time period in the full-screen image acquiring step isJPEG-compressed to create and accumulate a compressed full-screen image,a compressed full-screen image is not created until a lapse of apredetermined recording time period every time when a compressedfull-screen image is created, and the step goes to a subsequent step; afull-screen image transferring step in which a full screen data fileincluding the compressed full-screen image created in the full-screenimage creating step is created and the file is transferred to theserver; a splitting step in which the full-screen image data acquired inthe full-screen image acquiring step is split into block images of amatrix of eight by eight picture elements from one end of a screen area;a positional information creating step in which block images at twosequential time instants are compared in every block image split in thesplitting step to create positional information data expressing presenceor absence of a difference and positional information about a differencebased on sequential numbers of blocks; a parallel number calculatingstep in which a block determined as a block with a difference in thepositional information creating step is categorized into a differenceblock to calculate, from a number of difference blocks at an identicaltime instant, a number of parallel blocks to be horizontally arranged inorder to form a rectangle with the smallest margin by arranging allblock images of difference blocks at an identical time instant; acompressed difference image creating step in which a step is repeated inwhich the block images of the difference blocks in the number ofparallel blocks calculated in the parallel number calculating step arehorizontally arranged and then arranged on under side, an imagecollection in a rectangle with the margin blanked is created, thecollection is JPEG-compressed as one image, and compressed differenceimage is created and accumulated; and a difference image transferringstep in which a difference data file including the compressed differenceimage and pieces of positional information data is created and the fileis transferred to a server.
 13. The screen image transfer methodaccording to claim 12, wherein in the positional information creatingstep, in the comparison, a hash value is generated for each block imageand compared, a block with an unequal calculated value is categorizedinto a block with a difference, and a block with an equal calculatedvalue is categorized into a block with no difference; and the positionalinformation data is one byte data or two byte data in which a first onebit expresses presence or absence of a difference and seven bits or 15bits express a number of continuous blocks in which the presence orabsence of difference is the same.
 14. The screen image transfer methodaccording to claim 12, wherein the steps from the full-screen imageacquiring step to the compressed difference image creating step arerepeated until a lapse of the predetermined recording time period exceptthe full-screen image transferring step; and after the steps, instead ofthe compressed difference image transferring step, the method includesan accumulated image transferring step in which an accumulation datafile including the compressed full-screen image, the compresseddifference images accumulated until a lapse of a predetermined recordingtime period, and pieces of positional information data is created andthe file is transferred to a server.
 15. A reconstructing method for animage transferred to a server by the screen image transferring methodaccording to claim 12, the reconstructing method comprising: adifference block reconstructing step in which the image collection isreconstructed from the compressed difference image to reconstruct blockimages of difference blocks; and a full-screen image reconstructing stepof repeating a step for the predetermined recording time period in whichthe block image of the difference block is placed on a full-screen imageat a previous time instant based on the positional information data tocreate a full-screen image at subsequent time instant.